The long term objectives of this proposal are to define the microbial complexes that are mos compatible with periodontal health and devise therapeutic and/or preventive strategies to produce the desired plaque composition. Specific Aim 1 will determine the composition of supra- and subgingival plaque, the associations among species both within and between supra- and subgingival plaques, and seek differences between plaques from healthy and diseased individuals. In this cross-sectional study, 60 periodontitis and 30 periodontally healthy subjects will be assessed clinically at 6 periodontal sites per tooth. Supragingival plaque and subgingival plaque samples will be taken separately from the mesial aspect of each tooth and evaluated individually for their content of 80 bacterial species using checkerboard DNA-DNA hybridization providing 403,200 bacterial counts. Supragingival plaque control is thought to aid in the contro of periodontal infections, possibly by affecting subgingival plaque composition. Specific Aim 2 will determine the effect of repeated professional supragingival plaque removal on clinical parameters and subgingival plaque composition. In this longitudinal study, the 60 periodontitis patients from Specific Aim 1 will receive scaling and root planning (SRP) performed under local anesthesia. Thirty of these subjects, selected randomly, will receive professional supragingival plaque removal at weekly intervals for a period of months. All subjects will be evaluated clinically and for subgingival plaque composition (as described for Specific Aim 1) at 3, 6, and 12 months post SRP. Thus, an additional 403,200 bacterial counts will be determined. Data will be used to evaluate the effect of supragingival plaque control on the composition of subgingival plaque and the nature of the plaque composition associated with periodontal stability. The proposed studies will clarify the composition of supragingival plaque, extend the knowledge of subgingival plaque and provide a database for examining important bacterial associations in plaque. In addition the importance and biological basis of supragingival plaque control in the treatment and prevention of periodontal diseases and in maintaining stability of the periodontium will be determined.